Electromechanical transducer



FIG. 3

A. Al.. w. WILLIAMS ELECTROMECHANICAL TRANSDUCER Mii@ t 11W/Emme.r .ALFRED .w.w|LL| AMs Y BY um afmwm.

ATTORNEY l 6N l VOLTAGE SENSITIVE Q MENT FIG. 4

49/ ELE Feb. 14, 1950 Filed June 12, 194e Feb. 14, 1950 A; L. w. WILLIAMS 2,497,108

' ELECTROMECHANICAL TRANSDUCER Filed June .12, 1948 2 Sheets-Sheet 2 7 a2 8l e7 e6 i A/ j z 3 IH l Hlm! 93 es l 38 /7//// FIGB JNVENTOR. ALFRED L. W. Wl LLiAMS ATTORNEY Patented Feb. 14, 19,50

UNITED STATES PATENT OFFICE ELECTROMECHANICAL TRANSDUCER Application J une 12, 1948, Serial N0. 32,594

14 Claims. (Cl. 171-327 This invention relates to electro-mechanical transducers, and more particularly to such transducers comprising elements of electro-mechanically sensitive dielectric material.

Numerous types of elements of electro-mechanically sensitive dielectric material affording usefully high electro-mechanical response are known. Such elements may be cut in the form f plates or bars from single crystals of piezoelectric substances. Depending on the substance, on the crystallographic orientation of the plate or bar, and on the arrangement of electrodes applied thereto, the electro-mechanical transducing may involve any of several modes of mechanical motion of the element, such as thickness or lengthwise expansion, face or thickness shear, or flexural motion. Two expander bars may be electroded and electroded surfaces thereof c emented together in a known manner to form a bendingsensitive element in which one bar expands while the other contracts. In a similar manner two face-shear plates may be axed to each other to form a twisting-sensitive element.

Piezoelectric elements of the above-mentioned types have proved to be useful in many frequencyselective and transducing applications, but the shapes and sizes of the elements are limited by the desired crystallographic orientation and by the dimensions of Suitable single crystals which are found as minerals or which may be synthesized by practical methods. The electro-mechanical response of a transducer element in turn is limited by several factors, an important factor being the maximum dimensions in which the element is obtainable commercially. For example, if considerable electrical energy is available at a given voltage, it may be desired to transduce this energy to mechanical energy so as to obtain a large mechanical displacement. However, regardless of which of the above-mentioned types of piezoelectric element is used, the mechanical response in terms of meters of displacement per unit applied voltage is determined and limited by one of the dimensions of the element, for example the length dimension of a lengthwise expander bar. Certain cuts from a few types of synthetic single crystals may be made quite long, but the expense involved, the awkward size of the element, and the difficulty of mounting it to protect it from breakage make impractical the use of such an element in a transducer. Various mechanical lever systems are known for attachment to elements of the above-mentioned types in order to obtain or to utilize a specific mechanical motion in association with a crystal element 2 having a different motion. Nevertheless, considerations such as available power, impedance matching, and mechanical clearances restrict the mechanical transformations obtainable with lever systems.

There have been made available recently polycrystalline electro-mechanically-sensitive dielectric materials, which exhibit to a notable degree the property of developing substantial mechanical strains when subjected to an electrical field. The use of such materials, notably barium titanate bodies, which may be formed using ceramic techniques, has made it possible to produce transducer elements the size and shape of which are not limited by the dimensions of single crystals. Suitably polarized elements of polycrystalline titanate material are disclosed and claimed in the copending application Ser. No. 740,460, filed April 9, 1947, in the name of Hans Jaffe and assigned to the same assignee as the present invention. Bending-sensitive elements utilizing a plurality of mutually aflixed electroded titanate plates are disclosed and claimed in the copending application Ser. No. 740,461, filed April 9, 1947, in the name of Hans Jaffe and assigned to the same assignee as the present invention, this copending application having issued on October 18, 1949, as Patent No. 2,484,950. Transducers including titanate bender elements of non-linear cross-sectional shape and of elongated hollow or tubular shape are disclosed and claimed in copending applications Ser. Nos. 32,587 and 32,593, respectively, filed June 12, 1948, in the names of Charles K. Gravley and Alfred L. W. Williams, respectively, and assigned to the same assignee as the present invention. ments of these types may be used advantageously in electro-mechanical transducers and may be made to a rather large scale, the maximum dimensions and hence the electro-mechanical response of a transducer utilizing a polycrystalline element again are limited by considerations such asV awkwardness of shape and protection against breakage of a very long element.

Accordingly, it is an object of the invention to provide a. new and improved electro-mechanical transducer affording high electro-mechanical response and free from the above-mentioned limitations and disadvantages of prior transducers.

It is another object of the invention to provide a new and improved electro-mechanical transducer of'convenient size and shape for obtaining a high mechanical response from a given source of electrical energy.

It is a further object of the invention to provide While polycrystalline elea new and improved electro-mechanical transducer'utilizing an electro-mechanically sensitive element of polycrystalline dielectric material.

It is a still further object of the invention to provide a voltage-operated relay comprising an electro-mechanical transducer affording a high mechanical response to electrical excitation.

In accordance with the. invention, an electromechanical transducer comprises an elongated element of electro-mechanically sensitive dielectric material convoluted into a space the largest dimension of which is a small fraction of the length measured along the elongated element to provide an electro-mechanical response significantly greater 'than that of an element of the same material and cross-sectional shape having a length equal to the largest dimension of the space containing the convoluted element but having a straight configuration.

For a better understanding of the present in\ vention, together with other and further objects thereof. reference is had to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

In the drawings, Fig. 1 is a perspective view of an electro-mechanical transducer in the form of a voltage-operated relay embodying the invention; Figs. 2 and 3 are enlarged cross-sectional views showing alternative structures of the electro-mechanically sensitive element included 'in the Fig. 1 arrangement; Fig. 4 is a schematic circuit diagram of a fluorescent lighting system including an electro-mechanical transducer of the type illustrated in Fig. 1; Figs. 5 and 6 are plan and elevation views respectively of another electro-mechanical transducer embodying the invention; and Figs. 7 and 8 are plan and sectional elevation views respectively of an additional embodiment of the invention, the sectional view of Fig. 8 being taken along the line indicated 8-8 in Fig. 7.

Referring now to Fig. 1, there is illustrated in perspective view a voltage-operated relay including an electro-mechanical transducer embodying the present invention. This transducer comprises an elongated element II of electro-mechanically sensitive dielectric material having a convoluted configuration. More particularly, the element II is coiled into a generally helical configuration occupying a generally cylindrical space having a radius equal to the radius of the individual turns of the helical element II and having an axial length equal to the axial length of the helix formed by the element. The helical element is shown .in Fig. l with the central turns of the helix broken away to show details of construction. The exact number of turns is dependent upon particular design considerations such as available voltage. desired displacement of the relay contactor during operation, and the material and cross-sectional shape of the element. As illustrated in Fig. 1, the axial length of the cylindrical space occupied by the element is the largest'dimension of this space. This largest dimension of the space into which the elongated element is convoluted is a small fraction of the length measured helically along the elongated element.

While some elongated electro-mechanically sensitive elements of the types illustrated in the drawings. and particularly in Figs. 'l and 8 as described hereinbelow, may be machined from a single crystal of a piezoelectric material, the convoluted shape of the elements makes the use of polycrystalline electro-mechanically sensitive dielectric materials more practical. As mentioned hereinabove, such polycrystalline materials, notably a material consisting primarily of barium titanate. may be formed by the use of ceramic techniques. The material is inexpensive, and these forming techniques may be much more economical than the necessarily more or less complicated machining operations. The polycrystalline materials have the added advantage that they may be polarized in the thickness direction throughout the length of a shape which is convoluted in the longitudinal direction.

To provide support for the helical element Il and for the moving parts of the relay a framework is used, including a lower ring I2, three rods I3, Il, I6 equally spaced about the periphery of the cylindrical space the lower end of which is defined by the ring I2, and an upper disk I1 to the rim of which the three rods are fastened. During assembly the helical element II is slid over the rods I2, I4, and I8. As a means for mounting one end portion of the convoluted elongated element I I there is provided a yoke I8. The upper end of the yoke I8 has a hole through which the rod I3 passes, while the lower end is screwed to the ring I2 after the inner surface of one end portion of the element I I has been placed against the rod I3. Before the yoke Il is screwed to the ring I2, shims may be placed between the yoke and the ring so that the yoke barely touches the outer surface of the element Il. A cement such as a polymerizing phenolic cement then is inserted between and around the element, the rod I3, and the yoke I2 to anchor the end ofthe element. To facilitate fitting the element around the rods Il., Il, and I6, the outer surfaces of the rods may be covered with a soft material, preferably felt or other fabric having a surface com'- prised of many laments on top of which the element II rests. Pairs of pins such as the pins I9, I9 on the rod I8 near the mounted end of the element and the pins 2i, 2| on the rod I3 near the free end of the element may be inserted in holes in tliie rods to serve as guides for the helical elemen .Aillxed to the other or upper end portion of the element II is a movable contactor arrangement. Since the desired motion of the free end of the element is substantially peripherally of the cylinder defined by the helical element, it is advantageous to convert this peripheral motion into a rotary motion of a suitable shaft 22. A central hole through the disk I1 serves as a bushing for the shaft 22, and the shaft is maintained 55 in the bushing by a collar 23 screwed to the shaft above the disk I1 and by another collar, not visible in the drawing, screwed to the shaft below the disk. The lower end of the shaft 22 passes through a hole in an arm 24 which is adjustably tightened on the shaft. The arm 24 reaches radially outward as far as the radial distance to the outer surfaces of the rods I3, I4, and I6. A yoke 28 is passed over the outer surface of the upper end portion of the element II and c fastened with appropriate radial adjustment '4 the arm 2l by means of screws. A cement then is flowed between and around the element, the yoke 2t, and the end of the arm 24. -A contactor arm 21 of electrically nonconductive material is 70 fixed to the upper end of the shaft 22 and extends radially outwardly of the disk I1. A contactor 28, movable with the arm 21, is aillxed to the outer end of the arm 21. A bar 29 of electrically nonconductive material, adjustably attached by 75 means of screws to the disk I1, carries on its outer end a normally fixed contactor 3| in a position opposed to the movable contactor 28. 'The contactor 28 is adapted to occupy two positions, one position when the transducer element il is supplied with an excitation voltage and another position when the transducer is electrically unexcited. Excessive motion of the arm 21 in the direction toward the unexcited position is prevented by a stop member 32 fastened to the rim of the disk l1. The xed contactor 3| is adapted to be inelectrical contact with the movable contactor 28 when the arm 21 carrying the movable contactor moves into and occupies the electrically excited position. Connected to the contactors 28 and 3l are respective lead wires 33 and 34 leading to the terminals 36 and 31 respectively.

Referring to Fig. 2, a cross-sectional view taken anywhere along the element Il is shown. In the Fig. 2 embodiment the elongated element is a composite one made up of an inner longitudinally extending helical strip 4|, which advantageously is of an electro-mechanically sensitive polycrystalline material, and an outer longitudinally extending helical strip 42, which may be of the same material. The strip 4| just fits inside the strip 42, and the strips are cemented together along the contiguous, longitudinally extending, electroded faces thereof, providing a central electrode 43. The strips 4| and 42 also have electrodes 44 and 46 respectively on the exposed major surfaces thereof. An element of this type may have the general structure disclosed and claimed in the aforementioned copending application Ser. No. 740,461 of Hans Jaffe. If a titanate material is used, a suitable polarizing or biasing voltage may be maintained continuously across the helical strips 4| and 42 in the manner described and claimed in the aforementioned Icopending application Ser. No. 740,460 of Hans Jaffe. .With suitable titanate materials the continuous application of a biasing potential `may be avoided in some cases by resorting to a prepolarizing treatment; For this treatment a temporary connection may be made to the central electrode 43 and a rather high polarizing poten-l Fig. 1 apparatus, the temporary connections are 1 broken and the inner and outer electrodes 44 and 46 respectively may be connected individually by means of respective lead wires 41 and 48 to terminals 49 and 5| respectively. The polarizing treatment described hereinabove polarizes the titanate material of the strips 4| and 42 in opposite directions,l so that the application of an excitation voltage acrossthe terminals 49 and causes an excitation field inthe direction of polarization of one of the strips 4|, 42 and simultaneously in the direction opposite to the direction of polarizationin the other of the strips.`

An alternative cross-sectional shape for the element |I of Fig. 1 is illustrated in Fig. 3. Here there is shown an elongated hollow element of generally elliptical cross-sectional shape. Forming the wider and flatter sides of this elliptical shape are two opposite walls 53 and 54 of the element, of which the wall 53 may be the inner wall of the helical element The hollow element has a central or internal electrode 56 and two peripherally separated exposed electrodes 51 and 58 adjacent the exposed surfaces of the inner respective filaments.

and outer walls 53 and 84 respectively and extending longitudinally of the element. Titanate transducer elements of this general shape are disclosed and claimed in the aforementioned copending application Ser. No. 32,593 of Alfred L. W. Williams. An element of a suitable titanate material and of the type illustrated in Fig. 3 may be prepolarized, for example in a direction from the central electrode 56 outward toward both outer electrodes, by interconnecting 4temporarily the outer electrodes 51 and 58 and applying a rather high polarizing potential between these interconnected electrodes and the central electrode 56. The polarizing connections then are removed and the exposed electrodes 51 and 5I connected to the lead wires 41 and 48 respectively, leading to the terminals 49 and 5| respectively, as with the Fig. 2 element. Application of an exciting potential across the terminals 49 and 5| then causes an exciting field in a direction outward of the hollow element across one of the sides 53, 54 thereof and in a direction inward of the hollow element across the other side thereof. The central electrode 56 assumes under these circumstances an intermediate potential. With either the Fig. 2 or Fig. 3 element, the exposed electrodes 44, 46 or 51, 58 may be scraped of! or covered by insulating material where they pass under the yokes |8 and 26 near the ends of the element in the Fig. 1 arrangement to prevent short-circuiting of the electrodes and grounding to the supporting structure.

The schematic diagram of Fig. 4 illustrates an advantageous use of the voltage-operated relay of Fig. 1, and will be referred to in describing the operation of the Fig. 1 arrangement. The transducer element is indicated in the diagram of Fig. 4 by a box identified as a voltage-sensitive element. The mechanical coupling through the arm 24, shaft 22, and arm 21 to the movable contacter 28 is represented by a dashed line 6I, this mechanical coupling enabling motion of the movable contactor 28 relative to the fixed contactor 3|. The relay terminals 36 and 31 and the excitation terminals 49 and 5| of the element appear in the diagram of Fig. 4.

Therelay is a part of a fluorescent lighting arrangement including a fluorescent lamp 62 having filaments 63, 64 at opposite ends thereof and anode electrodes 66, 61 associated with the One side of the filaments 63 is connected to the terminal 31 and, through a glow discharge tube 68, to the terminal 5|. One side of the filament 64 is connected to the terminals 36 and 49. The fluorescent lighting system is supplied from an alternating current line 1|, to which it may be connected by closing a line switch 12. More specifically, the line 1| may be connected through the line switch 12 to a voltage step-up autotransformer 13. A cury rent-limiting inductor 14 is in circuit with the secondary terminals of the autotransformer 13.

The transformer secondary and the inductor 14 are connected across the sides of the filaments 83 and 64 which are not connected to the relay as described hereinabove.

When the line switch 12 is closed, a voltage which is high relative to the voltage of line 1| is placed across the lamp 62. Since the lamp is not conducting and the filament circuit through the relay contacts is open, this voltage appears also across the glow tube 68 and the element Il, causing a glow discharge in the glow tube. After the initiation of the glow discharge most of the 'Il secondary voltage of the autotransformer 13 ap-.

'7 pears across the element During the half cycle of the alternating-current wave which has the proper polarity an exciting field is impressed across the element tending to make the inner portion 4| or 53 (Fig. 2 or Fig. 3) of the .titanate element expand and the outer portion 42 or 54 contract. This involves in turn a lateral bending of each portion of the length of the coiled element with an associated increase in the radius of curvature along the entire length of the elemen't. The element may be sai/d to uncoil somewhat, and the uncoiling motion not only tends to increase the diameter of the helical element .with an outward motion of the side o! the helix opposite the rod I3 to whichthe bottom end of the helix is fixed, but also tends to causea pe- Y' ripheral motion of the helix in a counterclockwise direction as viewed from the top of the helix. Since the bottom end of the helix is fixed and the helix is wound upwardly in a clockwise sense. this counterclockwise motion is needed to make up the increased periphery of each turn of the helix. The resulting peripheral motion of each turn is added to that of the next higher turn.

Thus the arm 2l imparts a considerable counterclockwise rotation to the shaft 22, causing the movable'contactor 28 to come into contact with the fixed contactor 3| before the alternating voltage reaches its peak value in the half cycle under consideration. When the relay conthe cylindrical space occupied by the helix multiplied by the number of turns of the helix, and this very long element, having a straight conguration and mounted or clamped at one end, would exhibit upon electrical excitation a bending throughout its length with corresponding lateral displacement of the free end. This displacement would be 'of the same order of magnitude as the displacement of the free end of the helical element il tending to move the arm 24 and rotate the shaft 22. However, an ele=l ment of the extreme length of such a straight element would be entirely-impractical for most applications. Since the largest dimension usually limits the use of a transducer, the performance of the helical element should be compared with the performance of an element of the same material and cross-sectional shape having a length equal to the largest dimension, that is the axial dimension, of the helix but havingr a straight configuration. The magnitude of the electro-me- Hence appreciable heating of the filaments 63' and |54l occurs before a large number of cycles ofthe alternating current have passed. It is preferable that the fluorescent lamp 62 be of a type which may be ignited before its laments have become very warm. Accordingly, during the last of a limited number of cycles of the 'alternating current the filaments become warm enough for operation of the lamp. When the relay contacts open during this cycle', the flow of current through the now warm filaments and the inductor 'I4 is interrupted. The interruption of this current' causes a high voltage to be induced in the inductor 14, and the lamp 62 lights. The lamp current thereafter results in such a voltage drop across the inductor 14 that there is insufficient voltage across the glow tube 68 to ignite vthe tube, and the relay remains open as long as the lamp remains lit. Since there are no thermally operated elements in this fluorescent lighting arrangement other than the filaments 63 and 64 of the lamp itself, the period of starting of the lamp is limited primarily only by the desired extent of the heating of the filaments. For this reason lamp starters utilizing a voltageoperated relay operate more quickly than the conventional starter with `a bimetallic element in the starter circuit. l

The helical ele'ment whether of the type illustrated in Fig. 2 or Fig. 3. is a bending-sensitive element by virtue of the simultaneous tendencies of one side of the element to contract and of the other side to expand. If the element were straightened out it would have a length practically equal to the circumference of chanical response provided by the helical element then is significantly greater than the magnitude of theresponse of a straight element"` of the last-mentioned length, although the maximum dimension of the helical element is the same. More specifically, the mechanical response of the helical element, and hence of the movable contactor 28, for a given excitation voltage is significantly greater than that of a straight element of the same material and cross-sectional shape having a length equal to the axial length of the helix. While transducer structures including either convoluted or straight electro-mechanically sensitive elements may be designed to utilize mechanical resonances, the resonant frequencies and the electro-mechanical responses at resonance diier considerably for different designs, and the performance of convoluted and straight transducer elements is compared best at non-resonant frequencies, for example a very low frequency. It will Ibe evident to those skilled in the art that an electro-mechanical transducer including a convoluted element such as the element I| easily may be made to respond differently to electrical signals of different amplitudes,

since the displacement ofthe free end of thev element tends to be proportional to the amplitude of the applied voltage, and also that the converse electro-mechanical response may be utilized, whereby motion of the free end of the element causes a voltage to appear across the terminals 49 and 5|.

Referring now to the alternative transducer of the voltage-operated relay type illustrated in plan and elevation by Figs. 5 and 6the transducer shown comprises an elongated element 8| coiled into a generally spiral configuration occupying a generally circular or disk-shaped space the diameter of which is a small fraction of the length measured spirally along the elongated element. The coiled element again may have either of the bending-sensitive cross-sectional configurations illustrated in Figs. 2 and 3. The outer end portion of the spiral element 8| passes through a bracket 82 adjustably fastened by means of screws to a xed post 83. The bracket 82 is adjusted so as barely to touch the sides of the element 8|. The bracket then is tightened on the post 83, and cement is inserted between the contiguous surfaces of the element and of the bracket and post. The free inner end portion of the spiral element lies between the arms of a yoke structure 8|, which is a part of a contactor arm 86, and is cemented to the yoke 9 Il. The arm 30 is aiilxed to a rotatable shaft 01 riding in a thrust bearing Il. The remote end o! the arm l is twisted to accommodate a movable contactoil 3|, which is electrically insulated from the arm.

Electrical excitation of the electrodes on the exposed faces of the spiral element is accomplished by applying a. suitable voltage across the terminals I3 and 0|, whence the exciting potential is conveyed through conductors 41 and l0 respectively to the inner and outer electrodes respectively on the element 3|. similarly to the Fig. 1 arrangement. These electrodes are provided as illustrated in the cross-sectional view of Fig. 2 or 3, but are omitted in Figs. 5 and 6 for simplicity ol illustration. When the polarity of the exciting voltage is such as to cause the element to bend so as to increase the radius of curvature lof each portion of the spiral, the turns of the spiral as viewed in Fig. 5 tend not only to increase in diameter but also to rotate in a counter-clockwise direction. This results in a counter-clockwise rotation of the shaft 31 and lcauses the movable contactor 3| to move into contact with a fixed contactor 32 mounted on an insulating post 33. The relay circuit is conipleted through lead wires 33, 34 and terminals 30, 31, as in the Fig. 1 arrangement.

In a manner analogous to the operation of the helical element of the Fig. l arrangement the motion of each turn of the spiral element 3| is added to the motion of the next turn, resulting in a net displacement of the free end of the element much greater than the displacement of a single turn or portion of a turn. When the largest dimension of the transducer primarily determines its usefulness, as is frequently the case, the electro-mechanical response oi the spiral element should becompared with the response of a straight element having a length equal to the largest dimension of the lspiral element. this dimension being the diameter oi the generally circular space occupied by the spiral. The coiled configuration again provides a signiilcantly greater response for the spiral.

Figs. 7 and 8 illustrate in plan and sectional views a transducer including an elongated element |00 of electro-mechanically sensitive di-v electric material which, although not coiled' as are the helicaland spiral elements of the embodiments of Figs. 1-3 and Figs. 5-6 respectively, is convoluted in another manner into a space the largest dimension of which is a small iraction of the total length. of the element. The ele- Y ment I 00 may be cut froma plate or block of any of the electro-mechanically sensitlvematerials referred to hereinabove which is expansion-sensitive, that `is, whichy exhibits a longitudinal expansion or contraction under the influence of a lateral ileld. v The element III. in' the form illustrated in Figs. 7 and 8, comprises a series of seven relatively .straight legs, indicated consecutively. |0||01^in thel drawing. The bottom` portions of legs |0| and |32 are connected together, the top' portions oflegs |32 and |03 are connected together, thelbottom portions of legs` |03 and I are connected together, etc.,. forming a convoluted structure made up of the straight legs joined together progressively -at alternate ends vthereof by portions curved through approximately 180 degrees and made of the same dielectric material of which the legs themselves are made.

Conductive electrodes are placed adjacent each side of each les of the element |00, that is, on

5 which may be applied to the dielectric material in very thin layers. Such electrodes, in fact. may be used in the arrangements of the other figures. Although the electrodes ordinarily would be too thin to appear in the view of Fig. 7, the

l0 thickness of the electrodes is exaggerated in this view for purposes of illustration; to prevent complication of the drawings the electrodes are not separately distinguishable in the Pig. 8 view. Referring to Fig. 7, electrodes numbered |I|, H2,

H3, iii, and il! are placed respectively on the left and right side of leg Ill, the left and right sides of leg |02, and the left side of leg |03. Similar electrodes appear on the remaining sides of the several legs. lThe electrodes are connected in the following manner.

The end electrode the electrodes H4 and ||5 between the less |02 and- |03, and the electrodes between the legs |00 and |03 and between the legs |06 and |01 are interconnected and brought out to an excitation terminal 43. The remaining electrodes, includding the electrodes ||2 and ||3 between the legs |0| and |02 and the end electrode on the leg |01, are interconnected and brought out to the other excitation terminal 5|. .In this way alternate legs of the element |00 may be excited in opposite polarities at a given time. The start or upper end of the rst leg |0| is cemented Within a yoke ||1 which is part of a fixed bracket, while the end or bottom of the last leg |01 is cemented :l5 within a yoke ||3 carrying a movable contacter Application of an excitation potential of the proper polarity across the terminals and 5| causes a ileld to be applied across the leg |0| 4,0 through electrodes and ||2, resulting in the longitudinal expansion of that leg and a downward displacement of the bottom portion common to the legs |0| and |02. However, the leg |02 is excited through electrodes ||3 and 'lil by an electrical field of the opposite polarity, so that the top portion common to legs |02 -and |03 isl displaced downwardly not only by the amount of the downward displacement of the bottom of leg |02 but also by an approximately equal addltional amount ydue to the contraction of the leg |02. Leg |03 again is excited to produce an expansion, so that the bottom` portion common to legs |03 and |04 moves downwardly about three times as far as the bottom4 portion common to the legs |0| and |02'. In this 'manner the bottom and top portions of 'each successive leg receive accumulatively greater ,downward displacements. Therefore, the bottom end of the last leg |01V imparts a displacementto the. mov- $0 able contactor IIS significantly greater than the y, displacement of the bottom of the first leg |0l, althoughthe ilrst leg has a length nearly equal to the largest dimensionv of the convoluted transducer element.

$5 The-downward displacement ofthe contactar .I I9 moves it into contact with `a ilxed contactor |20. As in the arrangements of the previous v` iigures, the'movable and fixed contactors ||0 and |20 are provided with respective lead wires 33 and 3l connected to terminals 36 land 31 respectively to provide the conventional relay connections.4 To support and guide the element |00, two 'comb-shaped members |22 and |23 are mounted in ilxed positions near the top and bottom respectively of the convoluted element as viewe'd in Fig. 7. The areas between the teeth of the comb may be lined with a resilient fabric to receive and support the legs of the element with a minimum of opposition to the expansive motions thereof tending to close and open the relay contacts. v

The convoluted elements of the several embodiments of the invention described and illustrated hereinabove may be formed of any suitable electro-mechanically sensitive dielectric materials in any convenient manner. Of course, the proportions, dimensions, and number of convolutions of the elements may be varied to suit individual requirements. Accordingly, the various parts of the arrangements illustrated in the drawings may be made to a larger or smaller scale, as desired, and additional convolutions may be added to obtain still greater mechanical responses. The following are suggested merely as examples of various possible methods of manufacturing the convoluted elements. The helical element of Figs. 1 and 2 may be made by forming two hollow cylinders of titanate material with the outer diameter of one cylinder equal to the inner diameter of the other. 'Ihe outer surface of the smaller cylinder and the inner surface of the larger cylinder are coated with a cementing substance and the smaller cylinder is slipped within the larger cylinder. After the cement h-as hardened, helical slots are machined in the composite cylinder, leaving a helical element having the cross-sectional shape illustrated in Fig. 2. To obtain the cross-sectional shape illustrated in Fig. 3, a layer of raw titanate material may be deposited from suspension onto a ilat form bent into a spiral or helical configuration, and the resulting shape may be fired at ceramic-ilring` temperatures to form the helical tubular element with vaporization of the material of the form, in accordance with the method disclosed and claimed in the copending application Serial No.` 32,588, illed June 12, 1948, in the name of Charles K. Gravley and assigned to the same assignee as the present invention. A hollow element having the spiral configuration illustrated in Figs. 5 and 6 also may be formed by the method of the last-mentioned copending application. A block of any expansionsensitive electro-mechanically sensitive material may be used to fabricate the convoluted element illustrated in Figs. 7 and 8, the grooves separating the adjacent pairs of legs of the element being cut out byA means of a diamond saw.

While there have been described what are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modiflea-tions may be made therein without departing from the invention. and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

l. An electro-mechanical transducer comprising: an elongated element of electro-mechanically sensitive dielectric material convolutedinto a space the largest dimension of which is a small fraction of the length measured along said elongated element to provide an electro-mechanical response significantly greater than that of an element of the same material and cross-sectional shape having a length equal to said largest dimension but having a straight configuration.

2. An electro-mechanical transducer comprising: an elongated element of electro-mechanically sensitive dielectric material coiled into a l2 space the largest dimension of which is a small' fraction of the length measured along said elongated element to provide an electro-mechanical response significantly greater than that of an element of the same material and cross-sectional shape having a length equal to said largest dimension but having a straight configuration.

3. An electro-mechanical transducer comprising: an elongated element of electro-mechanically sensitive dielectric material coiled into a generally helical configuration occupying a generally cylindrical space the largest dimension of which is a small fraction of the length measured helically along said elongated element to provide an electro-mechanical response significantly greater than that of an element of the same material and cross-sectional shape having a length equal to said largest dimension but having a straight coniiguration.

fi. An electro-mechanical transducer comprising: an elongated element of electro-mechanically sensitive dielectric material coiled into a signicantly greater than largest dimension but having a straight configugenerally spiral coniiguration occupying a generally circular space the diameter of which is a small fraction of the length measured spirally along said elongated element to provide an electro-mechanical response signicantly greater than that of anl element of the same material and cross-sectional shape having a length equal E? said diameter but having a straight configura-"- on. I 5. An electro-mechanical transducer comprising: an elongated bending-sensitive element of electro-mechanically sensitive dielectric material coiled into a space the largest dimension of which is a small fraction of the length measured along said' elongated element tc provide an electromechanical response, involving bending of said bending-sensitive coiled element and associated changes in the radius of curvature of said coiled element, of a magnitude signiiicantly greater than the magnitude of the electro-mechanical response of an element of the same material and crosssectional shape having a length equal to said ration.

6. An electro-mechanical transducer comprising: an elongated hollow elementl of electromechanically sensitive polycrystalline dielectric material, having an internal electrode and two peripherally separated longitudinally extending exposed electrodes, and coiled into a space the largest dimension of which is a small fraction of the length measured along said elongated element to provide an electro-mechanical response that of an element of the same material and cross-sectional shape having a length equal to said largest dimension but having a straight conguration.

7. An electro-mechanical transducer comprising: an elongated composite element of electromechanically sensitive polycrystalline dielectric material, having two longitudinally extending strips cemented together along longitudinally extending electroded surfaces thereof, and coiled into a space the largest dimension of which is a small fraction of the length measured along said elongated element to provide an electro-mechanical response signicantly greater than that of an element of the same material and cross-sectional shape having a length equal to said largest dimension but having a straight configuration.

8. An electro-mechanical transducer comprising: an elongated expansion-sensitive element of 7l electro-mechanically sensitive dielectric material equal to said 13 convoluted into a which is a small fraction of the length measured along said elongated element to provide an electro-mechanical response signiiicantly greater than that of an element of the same material and space the largest dimension of cross-sectional shape having a length equal to said largest dimension but figuration.

9. An electro-mechanical transducer comprising: an elongated expansion-sensitive element of electro-mechanically sensitive dielectric material convoluted into a series of relatively straight legs joined progressively at alternate ends thereof by portions curved through approximately 180 degrees and occupying a space the largest dimension of which is a small fraction of the length measured along said elongated element to provide an electro-mechanical response significantly greater than that o! an element of the same material and cross-sectional shape having a length largest dimension but having a straight configuration.

10. An electro-mechanical transducer comprising: an elongated element oi' electro-mechanically sensitive polycrystalline dielectric material convoluted into a space the largest dimension 'of which is a small fraction of the length measured along said elongated element to provide an electro-mechanical response .significantly greater having a straight conthan that of an element of the same material and cross-sectional shape having a length equal to said largest dimension but having a straight configuration.

v11. An electro-mechanical transducer comprising: an elongated element of electro-mechanically sensitive polycrystalline titanate dielectric material convoluted into a space the largest dimension of which is a small fraction of the length measured along said elongated element to provide an electro-mechanical response significantly greater than that of an element of the same material and cross-sectional shape having a length equal to said largest dimension but having a straight configuration.

l2. An electro-mechanical transducer comprisl ing: an elongated element of electro-mecham cally sensitive polycrystalline barium titanate material convoluted into a space the largest dimension of which is a small fraction of the length measured along said elongated element to provide an electro-mechanical response significantly greater than that of an element of the same material and cross-sectional shape having a length equal to said largest dimension but having a straight configuration.

13. An electro-mechanical transducer comprising: an elongated element consisting primarily of polycrystalline barium titanate and convoluted into a space the largest dimension of which is a small fraction of the length measured along said elongated element to provide an electro-mechanical response signiiicantly greater than that of an element of the same material and cross-sectional shape having a length equal to said largest dimension but having a straight configuration.

14. A voltageoperated relay comprising: an electro-mechanical transducer including an elongated element of electro-mechanically sensitive dielectric material convoluted into a space the largest dimension of which is a small fraction of the length measured along said elongated element to provide a mechanical response for a given excitation voltage signiflcantly greater than that of an element of the same material and cross-sectional shape having a length equal to said largest dimension but having a straight configuration; means for mounting one end portion of said convoluted elongated element; a movable contactor ailixed to the other end portion of said element and adapted to occupy two positions, one position when said transducer is supplied with an excitation voltage and another position when said transducer is electrically unexcited; and a normally fixed contactor adapted to bein electrical contact with said movable contactor when said movable contactor occupies one of said two positions.

ALFRED L. W. WILLIAMS.

No references cited. 

